1. Field of the Invention
The present invention relates to a novel underwater processing apparatus and an underwater processing method, as well as to an automatic underwater processing apparatus, and in particular to a device for and a method of carrying out cutting, grinding, welding and surface-treatment in order to install, repair and process equipments belonging to nuclear facilities, marine vessels, bridges or the like.
2. Related Art
Conventionally, in the case of underwater processing metal or nonmetal, for example, in the case of underwater welding, in a method of carrying out a covered arc welding in an atmosphere in which no water is displaced therefrom, that is, the so-called wet process, a defect such as blow-holes are likely to be formed in a joint part or the like, and accordingly, a problem in view of reliability has been raised. Further, in a dry type process in which a part to be welded is surrounded by a water drainage chamber in its entirety, water in the chamber is displaced with air or shield gas, and then welding which has been carried out on the ground is directly carried out within the chamber, the drainage chamber should have a shape corresponding to that of the part to be welded. Thus, the facility becomes expensive. Accordingly, a local dry process wherein a cave from which water is displaced locally around a part to be processed, is defined, and welding, surface-treatment or the like is carried out within the cave, (which process will be hereinbelow referred as xe2x80x9ca local shield methodxe2x80x9d), has been most prosperously used as an underwater processing method.
It is important for processing in the local shield process to stably displace water from the local shield, and accordingly, various methods have been proposed in order to stably displace water from the local shield. For example, Japanese Patent Laid-Open No. S49-799939 discloses such a method in which triple shield gas nozzles are used, a first jet nozzle jetting shield gas, a second jet nozzle jetting gas in the form of a high velocity jet stream, and a third jet nozzle jetting water in the form of a high velocity jet stream in order to create a stable gas phase zone in the shield.
Further, Japanese Laid-Open Utility Model No. S55-116785 discloses a welding torch having a skirt shape partition member made of carbon fibers or the like, and provided in a skirt portion of a local shield.
Further, Japanese Patent Laid-Open No. S56-141956 proposes a method in which a slidable solid wall is provided in the front end part of a jet stream welding nozzle, being separated from and opposed to a torch so that its front end is made into contact with a mother material by means of a processing mechanism (a spring) while another front end part of the nozzle front end part is opened.
Further, Japanese Laid-Open Patent No. S56-6782 discloses a method in which metal or nonmetal thin wires are bundled so as to be formed into an annular brush-like flexible wall. Heat-resistant stainless steel wires are preferably used as the metal thin wires, and carbon fibers are preferably used as the nonmetal thin wires.
However, in such a technical field that high quality is earnestly desirable for a processed part in a device belonging to, for example, a nuclear installation, affection by a bit of remaining moisture in a local shield would be caused. In a general utility field in which a marine vessel, a bridge or the like is repaired, it is desirable to obtain a highly reliable processed part. Finally, it is most desirable that the above-mentioned welding part is surrounded by the displacement chamber in its entirety, so as to obtain a processing part which is near, as possible as it can, to a processing part obtained by using a dry type process in which water in the displacement chamber is displaced with air or shield gas. However, it can be hardly achieved in the above-mentioned conventional technology. Japanese Laid-Open Patent No. S49-79939 discloses the provision of a third nozzle for jetting water at a high velocity so as to form a water curtain in order to prevent water from entering the local shield. However such a water curtain may not completely prevent water from entering into the local shield if a workpiece is complicated in its shape.
Further, in the method disclosed in the Japanese Laid-Open Utility Mode No. S55-116785, the pressing force of a welder relies upon a force adjusted by a worker himself, and accordingly, high skill is required for preventing water from entering. Further, repairing in a nuclear reactor can not be carried out by this method due to the presence of radio-active rays.
Further, in the Japanese Laid-Open Patent No. S56-141965, the slidable solid wall is not the one which completely shields the outer periphery of the torch in order to make contact with the mother material, and further, if the workpiece has a complicated shape, it would be impossible to completely prevent water from entering.
Further, in the Japanese Laid-Open Patent No. S56-6782, the flexible wall which is formed by bundling thin wires in a brush-like shape may not be completely prevent water from entering if a workpiece has a complicated shape.
An object of the present invention is to provide an underwater processing apparatus and an underwater processing method, which can effectively prevent water from entering a shield even though a workpiece has recesses and protrusions, and which can reduce variation of gas flow for a part to be processed, and also to provide an automatic underwater processing apparatus, and the application thereof to a nuclear reactor.
To the end according to the present invention, there is provided an underwater processing apparatus including a shield means for locally shielding a part to be processed of a workpiece with gas in an underwater environment in order to prevent water from entering the shield, for underwater processing the workpiece underwater, wherein the shield means is composed of a solid wall formed of a member having a slidable part making contact with the workpiece, and adapted to be made into contact with the workpiece and to be vertically movable by a pressing force, and a water jetting means for creating a water stream curtain around the outer periphery of the solid wall.
If the above-mentioned processing is accompanied with heating within the shield, it is preferable to introduce nonoxidative gas.
In combination of the water steam curtain, the gas shield around the solid wall according to the present invention, can prevent water from entering into a part to be processed, and the supply volume of gas for the gas shield can be reduced while variation in the supply volume of the gas can be decreased, thereby it is possible to stably carry out processing such as welding.
In particular, a stable gas shield is indispensable for welding with low input heat.
Further, according to the present invention, there is provided an underwater processing apparatus including a shield means for locally covering a part to be welded of a workpiece in order to prevent water from entering thereinto, in which nonoxidative gas is introduced into the shield means while a welding bevel of the workpiece is moved along a welding edge during welding, wherein an opening part is formed around the outer periphery of a torch for carrying out buildup welding in the welding bevel of the workpiece, facing the workpiece, a solid wall similar to the above-mentioned solid wall, formed of a slidable member is provided in a skirt part which makes contact with the workpiece so as to cover the entire welding width in a direction orthogonal to the direction of a welding line, and water jet nozzles for creating a water stream curtain around the outer periphery of the solid wall is provided. As a heat source, arc or laser may be used. The arc is more preferable for welding with low heat, using a high frequency pulse current.
Further, the above-mentioned water jet nozzles are provided along the welding bevel of the workpiece so as to be opened in front and rear of the welding bevel of the workpiece in the direction of the welding line, and are widened toward the welding bevel of the workpiece while having water jet ports which are longer than that of the width of the welding bevel of the workpiece. It is preferable that the water jet ports are opposed to the workpiece and have any one of a triangular shape, a rectangular shape, a polygonal shape, a crescent shape, an elliptic shape, a combination thereof.
Further it is preferable that the above-mentioned shield means has such a function that water is prevented from entering into the bevel of the workpiece, and the welding torch can be moved to and from the welding bevel of the workpiece, independent from the shield means.
Further, it is preferable that the shield means is provided with an illumination device for illuminating the interior of the shield means, an optical monitoring device for optically monitoring the interior of the shield means, a detector for detecting a pressure in the shield means so as to deliver an electrical signal indicating the pressure, and a control means for comparing the pressure with a preset pressure so as to control the pressure.
Further, it is preferable that the underwater processing apparatus is provided with a detector for detecting a water depth so as to deliver an electric signal, and is incorporated with a function in which the electric signal from the detector is converted into an underwater pressure.
The underwater processing apparatus according to the present invention can be used as a laser processing apparatus, a laser welding apparatus or a laser surface reforming apparatus.
Further, the underwater processing apparatus according to the present invention can be installed so as to be moved in an underwater environment on a rail or with no track, and accordingly, checking, inspection, grinding, repair and surface reformation of a structure can be carried out in the underwater environment. An underwater working machine incorporating this underwater processing apparatus is provided with a mechanism which allows it to move along a wall surface of the underwater structure, and further, the underwater working machine is provided with a working tool fixing part onto which an underwater tool unit is attached in order to carry out the above-mentioned underwater work.
Further, under remote-control from the outside of the underwater environment, the above-mentioned underwater working machine is sunk into the underwater environment and then set to a predetermined position in order to carry out ultrasonic flaw detection, shot-peening, water-jet peening, grinding and the like.
It is preferable that the above-mentioned welding torch according to the present invention can be moved to and from the welding bevel of the working piece, independent from the above-mentioned shield.
According to the present invention, there is provided an underwater processing apparatus comprising a torch having an arc electrode or a laser torch for projecting a laser beam, a torch body for supporting the torch, a solid wall provided on the workpiece side of the torch body so as to surround the entire periphery of the torch, and adapted to make contact with the workpiece and to be moved up and down by a pressing force, a water let nozzle provided to the torch body around the outer periphery of the solid wall, and a shield gas supply means provided to the torch body for jetting nonoxidative gas in said torch body so as to cover a part to be processed of the workpiece with the nonoxidative gas.
According to the present invention, there is provided an automatic underwater processing apparatus comprising an underwater processing apparatus in which a workpiece is locally covered with a shield member in an underwater environment while the shield member is filled therein with gas, and the shield member is covered with a water stream curtain jetted from a water jet nozzle provided around the outer periphery of the shield member while the workpiece is inspected or processed, a gas supply device which detects a pressure, a flowrate or the like of the gas fed from a gas bomb so as to supply the gas into the shield member under control of the supply volume of the gas, a water supply device for supplying water under control of water pressure or the like in accordance with a size of the welding bevel or the like, a water depth or the like, a drive device integrally incorporated with the underwater processing apparatus and is operated along an object to be inspected or processed, in accordance with inspection terms or manufacturing terms, and a control device for carrying out the above-mentioned inspection or process in accordance with a previously stored program or in follow-up to variation in the output thereof.
Further, according to the present invention, there is provided an underwater processing method in which a workpiece preferably having a welding bevel is locally covered, in an underwater environment, with a shield member which is filled therein with gas, preferably, inert gas, the outer periphery of the shield member is covered with a water stream curtain, and in this condition, the workpiece is inspected or process. It is preferable that the shield defined by the water stream curtain may not be provided for shielding the entire shield member, but be provided for shielding the welding bevel with a sufficient width in the direction of the processing or the inspection.
According to the present invention, there is provided a nuclear reactor composed of reactor interior components such as a shroud, a gas-water separator, a reactor core support panel, an upper grid panel, a shroud support, a control rod housing, and a control rod drive device housing, these components constituting the nuclear reactor are made of austenite group stainless steel, wherein at least one of these components is repaired through multi-layered buildup welding, and the area of the build-up welding is preferably from 0.1 to 5 mm2, and more preferably from 0.5 to 3 mm2, in section per one pass.
According to the present invention, there is provided a nuclear reactor repairing method of repairing at least one of the above-mentioned components constituting the nuclear reactor, wherein the component is locally covered in an underwater environment with a shield member which is filled therein gas, and the outer periphery of the shield member is covered with a water stream curtain while the above-mentioned multi-layered build-up welding is carried out with the use of a welding wire having a diameter of less than 1 mm, and preferably 0.4 to 0.8 mm, by a heat source preferably with 0.1 to 1.5 kJ/cm, and more preferably with 0.5 to 1 kJ/cm. Arc or a laser beam is used as a heat source. The arc for high frequency pulse welding of 1 to 20 kHz can carry out welding with a low input heat, and accordingly, repair welding with an extremely small heat affected zone (HAZ) can be made. The repair welding according to the present invention, can be carried out underwater, and accordingly, welding with substantially no HAZ can be carried out. Therefore, the welding after the repair can be directly used.
With the underwater processing apparatus according to the present invention, an arc is produced between a non-consumable electrode or a consumable electrode, which is located in the vicinity of a welding position, and a mother material by a main pulse current during build-up welding using high-frequency pulse arc welding, a reverse pulse current having a polarity different from that of the main pulse current is applied upon transient from the turn-on to the turn-off of the main pulse current, so as to the leading edge parts and the trailing edge parts of the main pulse and the reverse pulse are sharpened in order to form a directive arc, thereby it is possible to carry out welding with a low input heat.
It is preferable to prepare a current stopping period between the main pulse currents after the reverse current. It is preferable to apply a base current which is smaller than the main pulse current, between the main pulse currents after the reverse pulse current.
It is preferable to periodically change either the peak values of the main pulse current and the main base current or the energizing times of the main pulse current and the base current. It is preferable to periodically change the main pulse current with a period from several Hz to several ten Hz so as to agitate molten metal in order to inhibit grain growth.
It is preferable to change the main pulse current, the reverse pulse current and the base current, the energizing time and the current stopping time, independent from one another.
It is preferable to set the rise time and the fall time of the main pulse current to 50 xcexcsec.
It is preferable to incorporate, in the above-mentioned welding device, a power source for supplying the main pulse current for generating an arc between the non-consumable electrode or the consumable electrode, which is located in the vicinity of the welding position, and the mother material, a high frequency converting device for converting a d.c. current into high-frequency welding currents having different polarities, and a control device for applying the reverse pulse current having a polarity different from that of the main pulse current upon transient from the turn-on to the turn-off of the main pulse current, so as to sharpen the leading edges and the trailing edges of the main pulse current and the reverse pulse current in order to form a directive arc.
According to the present invention, there is provided an underwater pulse arc welding device comprising a welding torch incorporating an arc electrode, a pulse welding power source for producing a high frequency pulse current which periodically generates a high frequency pulse arc voltage at the arc electrode, and a servomotor, a torch drive part for adjusting a gap between the arc electrode in the welding torch and a mother material to be welded, an arc voltage detecting part for detecting a voltage between the arc electrode and the motor material to be welded, and a turn-on time averaging device for obtaining an average value of arc voltages in a time period from the time of initiation of rising to the time of completion of falling of the pulse arc voltage, wherein the torch drive part is preferably operated for adjustment so that an averaged voltage value during the turn-on period, obtained by the turn-on time averaging part becomes equal to an arc voltage reference value.
Further, according to the present invention, it is preferable to provide a low pass filter circuit for processing a waveform of the above-mentioned arc voltage, in addition to the means having the above-mentioned feature so as to obtain an averaged value over a turn-on time after the above-mentioned waveform process is carried out.